Electric motors are used in a host of robotic or other automated systems to provide a torque suitable for performing useful work in a system. Electric motors include a stator and a rotor, with either or both of these components having windings or coils for producing a magnetic flux when selectively energized by a power supply. The opposing magnetic fluxes of the stator and rotor ultimately produce the desired rotation of the rotor. The rotational force may be harnessed as needed to produce the desired torque within the driven system.
Electric motors come in a variety of alternating current (AC) and direct current (DC) designs. DC motors in particular may be of the brush type, the brushless type, or the stepper motor type, with each design having relative performance advantages. Of these, the brushless DC or BLDC motor eliminates windings from the rotor and thereby provides certain efficiency, durability, and noise-related performance advantages relative to other motor designs.
In a fail-safe electromagnetic braking system of the type commonly used with a BLDC motor, electrical power may be selectively applied to an electromagnet to actuate or release the brake depending on the design of the brake assembly. For example, one design applies a voltage to the coils of an electromagnet portion of the brake assembly, with the electromagnetic flux generated by the electromagnet ultimately cancelling a magnetic flux of a permanent magnet portion of the brake assembly. Once the respective fluxes are cancelled in this manner a brake pad disengages from frictional engagement with the rotor. Likewise, interruption of power transmission to the electromagnet allows the magnetic flux of the permanent magnet to move the brake pad into frictional engagement with the rotor, thereby applying the brake.
In conventional electromagnetic braking systems the main DC power supply providing electrical power to the motor is usually separate from the power supply used to energize the brake assembly. This is due in large part to the substantial difference between the motor voltage and the required brake release voltage. To optimize performance of a given electromagnetic brake assembly, a controller may apply a constant biasing force using DC power provided by the dedicated brake power supply. However, this practice may result in the generation of excessive heat in the brake assembly, a result that may affect certain heat-sensitive components positioned in proximity to any of the heated surfaces.